October 28, 2013

Fossilized Toe Prints Identified As Belonging To Large Ancient Bird

Scientists, publishing a paper in the journal Palaeontology, say two fossilized footprints found in Australia are most likely the oldest known bird tracks in the country.

The researchers said the thin-toed tracks in fluvial sandstone were most likely made by two individual birds that were the size of a great egret or a small heron. These ancient birds would have lived during the Early Cretaceous period.

"These tracks are evidence that we had sizeable, flying birds living alongside other kinds of dinosaurs on these polar, river floodplains, about 105 million years ago," Anthony Martin, a paleontologist at Emory University in Atlanta who specializes in trace fossils, said in a statement.

The footprint’s rear-pointing toes helped scientists distinguish the tracks as avian, as opposed to a third fossil track that was also found at the same site which belonged to a non-avian theropod. A long drag mark on one of the two bird tracks helped Martin analyze it even further (see image below).

"I immediately knew what it was – a flight landing track – because I've seen many similar tracks made by egrets and herons on the sandy beaches of Georgia," Martin says.

He said the footprint has a “beautiful skid mark” from the back toe dragging in the sand, which could have been caused due to the bird coming in for a soft landing. If these are indeed landing tracks then it could help deepen scientific understanding about the evolution of flight.

Modern-day birds actually share many characteristics with non-avian dinosaurs that went extinct millions of years ago. Martin has discovered the trace fossils of non-avian dinosaur burrows, including at a site along the coast of Victoria.

Tyrannosaurus rex, or “T. rex.,” had a vestigial rear toe, similar to birds today. Scientists like Martin say this feature shows that the T. rex shared a common ancestor with birds.

"In some dinosaur lineages, that rear toe got longer instead of shorter and made a great adaptation for perching up in trees," Martin said in a press release. "Tracks and other trace fossils offer clues to how non-avian dinosaurs and birds evolved and started occupying different ecological niches."

Dinosaur Cove in southern Victoria has given scientists a treasure trove of non-avian dinosaur bones from dozens of species, where the latest footprints were discovered. Martin discovered the first known dinosaur trackway of Victoria in 2010 and a few other tracks have been discovered since then. The tracks were made on the moist sand of a river bank, perhaps after a polar winter.

"The biggest question for me," he adds, "is whether the birds that made these tracks lived at the site during the polar winter, or migrated there during the spring and summer."

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Image Below: A drag mark made by the rear toe on one of the Cretaceous bird tracks indicates that it was a flight landing track. Credit: Anthony Martin